(PE-38079) Revert ffi bump

Puppet and Facter are confined, work is planned to be able to unpin that. Ship 15 in the meantime.

configs/components/rubygem-ffi.rb

@@ -11,8 +11,8 @@
     pkg.version '1.13.1'
     pkg.sha256sum '4e15f52ee45af7c5674d656041855448adbb5022618be252cd602d81b8e2978a'
   else
-    pkg.version '1.16.3'
-    pkg.sha256sum '6d3242ff10c87271b0675c58d68d3f10148fabc2ad6da52a18123f06078871fb'
+    pkg.version '1.15.5'
+    pkg.sha256sum '6f2ed2fa68047962d6072b964420cba91d82ce6fa8ee251950c17fca6af3c2a0'
   end
 
   instance_eval File.read('configs/components/_base-rubygem.rb')
@@ -59,7 +59,7 @@
       case pkg.get_version
       when '1.9.25'
         pkg.sha256sum '5473ac958b78f271f53e9a88197c35cd3e990fbe625d21e525c56d62ae3750da'
-      when '1.16.3'
+      when '1.15.5'
         pkg.sha256sum '9acc4e474bef25dbcf827b1e6fce4067e9a1eff74a0296d25f0af392fafcd096'
       end
 
@@ -70,8 +70,8 @@
       case pkg.get_version
       when '1.9.25'
         pkg.sha256sum '43d357732a6a0e3e41dc7e28a9c9c5112ac66f4a6ed9e1de40afba9ffcb836c1'
-      when '1.16.3'
-        pkg.sha256sum 'ee49ccfa125f84a2f2053a0e6dd8433a34233479e026513ecbf06798ba542fe6'
+      when '1.15.5'
+        pkg.sha256sum '6e52c39fdbbccc085ae05d489d1b835ce05dcdf2a4c88ba739e3b42afd2b5404'
       end
 
       pkg.url "https://rubygems.org/downloads/ffi-#{pkg.get_version}-x86-mingw32.gem"
@@ -157,4 +157,4 @@
       %(#{platform[:sed]} -i '0,/ensure_required_ruby_version_met/b; /ensure_required_ruby_version_met/d' #{base_ruby}/rubygems/installer.rb)
     end
   end
-end
+end